Phase transformations in nickel-rich nickel-titanium alloys

437 Pages·2007·11.98 MB·English

UC San Diego
UC San Diego Electronic Theses and Dissertations
Title
Phase transformations in nickel-rich nickel-titanium alloys : influence of strain-rate,
temperature, thermomechanical treatment and nickel composition on the shape memory
and superelastic characteristics
Permalink
https://escholarship.org/uc/item/7dt6n9p8
Author
Adharapurapu, Raghavendra R.
Publication Date
2007

Peer reviewed|Thesis/dissertation
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University of California
UNIVERSITY OF CALIFORNIA, SAN DIEGO

Phase Transformations in Nickel-rich Nickel-Titanium Alloys:
Influence of Strain-rate, Temperature, Thermomechanical Treatment and
Nickel Composition on the Shape Memory and Superelastic Characteristics

A dissertation submitted in partial satisfaction of the
requirements for the degree Doctor of Philosophy

in

Materials Science and Engineering

by

Raghavendra R. Adharapurapu

Committee in charge:
Professor Kenneth S. Vecchio, Chair
Professor Prabhakar R. Bandaru
Professor Sungho Jin
Professor John B. Kosmatka
Professor Robert O. Ritchie

2007
Copyright
Raghavendra R. Adharapurapu, 2007
All rights reserved
The dissertation of Raghavendra R. Adharapurapu is approved,
and it is acceptable in quality and form for publication on microfilm:

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Chair

University of California, San Diego
2007

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DEDICATION

Dedicated to
My Parents, who taught me how to speak
My Guru, who taught me how to be silent

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TABLE OF CONTENTS
Signature Page...............................................................................................................iii
Dedication......................................................................................................................iv
Table of Contents...........................................................................................................v
List of Figures...............................................................................................................xii
List of Tables.............................................................................................................xxiii
Acknowledgements...................................................................................................xxiv
Curriculum Vitae......................................................................................................xxvii
Abstract......................................................................................................................xxxi
1 INTRODUCTION................................................................................................1
1.1 General introduction.......................................................................................1
1.2 Motivation and Purpose of the study..............................................................3
1.3 Objectives.....................................................................................................11
1.4 Significance of the study..............................................................................13
1.5 Relevance to practical applications..............................................................16
1.6 Arrangement of the thesis.............................................................................17
1.7 Figures..........................................................................................................19
1.8 References....................................................................................................20
2 BACKGROUND.................................................................................................28
2.1 Basic Phenomenon.......................................................................................28
2.1.1 What is unique about NiTi alloy?.........................................................28
2.1.2 Brief History.........................................................................................29
2.1.3 Thermoelasticity and Martensitic Transformations..............................37
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2.1.4 Martensitic transformation in Ni-Ti alloys...........................................48
2.1.4.1 Crystal Structures of the austenite and the martensite phases..........48
2.1.4.2 Twinning...........................................................................................50
2.1.4.3 Twinning and Twins in NiTi............................................................56
2.1.4.4 Classification of twin types..............................................................60
2.1.4.5 Austenite-martensite interface..........................................................61
2.1.5 Effect of stress on the martensitic transformation................................68
2.1.6 Pseudoelasticity and Superelasticity.....................................................75
2.1.7 Shape memory effect: Origin and mechanisms....................................78
2.1.8 One-way, Two-way and All-round shape memory effect....................80
2.1.9 Rubber-like effect and Pseudoelasticity...............................................84
2.2 R-phase Transition........................................................................................86
2.3 Physical Metallurgy and Processing of NiTi alloys.....................................89
2.3.1 Phase diagram.......................................................................................89
2.3.2 Precipitation in NiTi alloys..................................................................91
2.3.3 Crystal structure of different precipitates.............................................92
2.3.4 Processing of Ni-Ti alloys: Effect of Ni composition..........................95
2.3.5 Tailoring transformation temperatures: Effect of various parameters102
2.3.6 Multiple-stage Transformations (MST).............................................104
2.4 Deformation behavior of NiTi alloys.........................................................111
2.4.1 Effect of temperature..........................................................................111
2.4.2 Effect of thermomechanical treatment...............................................115
2.5 Summary of Objectives..............................................................................119
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2.6 Figures........................................................................................................119
2.7 References..................................................................................................152
3 EVOLUTION OF MULTIPLE-STAGE TRANSFORMATIONS (MST) IN
NICKEL-RICH 50.8-NiTi: EFFECTS OF AGING AND COOLING RATE ON
THE SHAPE MEMORY CHARACTERISTICS.................................................178
3.1 Abstract.......................................................................................................178
3.2 Introduction................................................................................................179
3.3 Experimental...............................................................................................189
3.3.1 Materials and microstructure..............................................................189
3.3.2 Texture Measurements.......................................................................190
3.3.3 Experimental Procedure....................................................................193
3.4 Results and Discussion...............................................................................194
3.4.1 Phase Transformations: DSC Results.................................................194
3.4.1.1 As-Received: Transformation sequence.........................................194
3.4.1.2 Effect of aging Temperature (Aged+WQ): Evolution of MST......197
3.4.1.3 Effect of cooling rate......................................................................209
3.4.2 Stress-strain Response of NiTi...........................................................215
3.4.2.1 As-received: Stress-Strain Behavior...............................................215
3.4.2.2 Effect of Aging Temperature: Aged+WQ......................................216
3.4.2.3 Effect of Cooling rate.....................................................................219
3.4.3 Discussion...........................................................................................220
3.5 Conclusions................................................................................................224
3.6 Acknowledgements....................................................................................225
vii
3.7 Figures........................................................................................................226
3.8 References..................................................................................................240
4 HIGH STRAIN-RATE RESPONSE OF NiTi SHAPE MEMORY ALLOY:
A SYSTEMATIC INVESTIGATION OF TEMPERATURE EFFECTS ON
TENSION-COMPRESSION ASYMMETRY.......................................................248
4.1 Abstract.......................................................................................................248
4.2 Introduction................................................................................................249
4.3 Experimental Procedure.............................................................................253
4.3.1 Materials and Specimen.....................................................................253
4.3.2 Testing temperature............................................................................254
4.3.3 Quasi-static and high strain tests........................................................254
4.3.4 High strain rate compression with pulse shaping...............................255
4.4 Results and Discussion...............................................................................258
4.4.1 Stress-strain response of NiTi at 20OC: Effect of strain rate..............258
4.4.2 Dynamic stress-strain response of NiTi at elevated temperatures......261
4.4.3 Dynamic stress-strain response of NiTi at low temperature..............264
4.4.4 Compression–tension asymmetry.......................................................267
4.5 Conclusions................................................................................................271
4.6 Acknowledgements....................................................................................273
4.7 Figures........................................................................................................274
4.8 References..................................................................................................280
5 HIGH-STRAIN RATE RESPONSE OF 50.8-NiTi: INFLUENCE OF
THERMOMECHANICAL TREATMENT AND TEXTURE.............................285
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5.1 Abstract.......................................................................................................285
5.2 Introduction................................................................................................285
5.3 Textures in Ni-Ti alloys..............................................................................287
5.4 Experimental...............................................................................................292
5.4.1 Materials and microstructure..............................................................292
5.4.2 Starting Textures................................................................................294
5.4.3 DSC measurements............................................................................295
5.4.4 Testing temperature............................................................................296
5.4.5 Quasi-static and high-strain tests........................................................297
5.5 Results and Discussion...............................................................................298
5.5.1 DSC measurements............................................................................298
5.5.2 Tensile Stress-strain response of NiTi at 20oC: sheet vs. rod.............299
5.5.3 Quasi-static stress-strain response of NiTi: Effect of temperature....304
5.5.4 Dynamic stress-strain response of NiTi: Effect of temperature.........310
5.5.5 Dynamic response of 50.8Ni-Ti: Effect of TM..................................313
5.5.6 Fractography and fracture mechanisms..............................................316
5.6 Conclusions................................................................................................317
5.7 Acknowledgements....................................................................................319
5.8 Figures........................................................................................................320
5.9 References..................................................................................................331
6 MICROSTRUCTURE DEVELOPMENT IN Ni-RICH 55NiTi ALLOY:
AGING STUDIES ON PRECIPITATION REACTIONS AND SHAPE
MEMORY CHARACTERISTICS.........................................................................339
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